PROJECT ABSTRACT In the last decade, there has been expansion of both health information technology by healthcare systems and internet use by patients. This simultaneous growth provides a unique opportunity for healthcare systems to collect patient-reported outcomes (PROs) and integrate PROs into clinical care by using patient portals. Patient portals are secure websites that give patients access to their health information via a web connection. Early studies have found that patients who use portals have higher levels of satisfaction and engagement. To date, however, portals have not been used proactively by healthcare systems to systematically collect PROs. Population-wide proactive collection of PROs would be valuable for identifying and managing patients with depression. In primary care, major depressive disorder (MDD) is highly prevalent and is associated with reduced quality of life and suicide. However, only 50% of patients in primary care receive recommended annual screening, and only 50% of patients with MDD are treated adequately. Systematic measurement of MDD symptoms can lead to increased treatment and greater rates of remission; however, many providers do not routinely measure symptoms. The Computerized Adaptive Test for Mental Health (CAT-MH) is a recent innovation in depression symptom measurement that could allow for efficient assessments. The CAT-MH is a validated test that uses algorithms in real-time to ask the most diagnostically informative questions and assesses mental health symptoms, including depression. In general, CATs could be ideal for engaging patients in providing PROs because these tests are both very precise and very brief; however, to date, few CATs have been integrated into EHRs. This study's goals are to integrate the CAT-MH into an EHR for a healthcare system and evaluate the effectiveness of collecting depression symptoms via a patient portal (MyChart) vs. usual collection during clinic visits in two randomized controlled trials. In Aim 1, among primary care patients who are due for depression screening, we will determine whether MyChart CAT-MH depression screening (population-based care) increases the number of screenings, compared to usual care. In Aim 2, among primary care patients with active MDD, we will determine whether patients who receive MyChart depression measurement (measurement-based care) have higher rates of MDD remission, compared to patients who receive usual care. With these aims, this grant will provide essential information on the barriers and solutions to integrating adaptive tests for PROs into EHRs, as well as evidence for the capability of patient portals for providing proactive population-based patient-reported outcome measurement.